An explanation for the first question is that God is in control over everything and that everything happens because he has allowed it. Sometimes he strike people with afflictions, but that does not mean he really wants to do it. Note the word "willingly" in the second verse. He does not do it willingly, but that does not mean he doesn't do it.
An explanation for the second question is that it was Goliath's brother (since Goliath himself had already been slain). Note that names and relations was not as well recorded then as it is today. Also, the same writer would not make such a large mistake in this obvious example.
In this type of issue, where there might be doubt as to whether the translation is correct or not, it's a good idea to examine the original source and if that is not possible examine a number of different translations of the passage. I did this by looking up the verse in every English translation available at BibleGateway.com and found that the most of them uses the word "willingly". Many says that God does not enjoy doing it and some says that he does not do it by heart.